This invention pertains to devices to indicate that a tire is underinflated, and more particularly to such a device operated electrically and activated by the radial enlargement of an underinflated tire caused by the centrifugal force on the rotating tire and its tread.
There have been many devices adapted to indicate the deflation of a pneumatic tire on a vehicle. Many of these use mechanical signals and nearly all of those are mounted on the wheel itself. Some use electrical devices as signals, and if those are mounted on the wheel, it is necessary to use slip rings or similar devices to conduct an electrical impulse to a signalling device in the driver's area of the car. Most also either sense a reduction of pneumatic pressure or a increase in the breadth of the tire where it touches the ground.
My invention, however, comprises a device fixed to the vehicle itself so that electrical connections can readily be made. It depends for its signaling on the fact that an underinflated tire rotating at speeds of 25 miles per hour or more actually expands in diameter because of centrifugal force on the tread. At speeds of 40 miles per hour, I have measured an increase of as much as two inches in the diameter of an underinflated truck tire. My device requires much less expansion than that, and thus provides a device convenient to install and reliable in operation. Means can be provided to signal each tire individually, or all the activating devices may be attached to a single signal.